Type viewcontroller does not conform to protocol "uiViewControllerAnimatedTransitioning"

//
//  TransitionAnimator.swift
//  Junaid Abdurahman
//
//  Created by Junaid Abdurahman  on 2015/04/23.
//  Copyright (c) 2015 Junaid. All rights reserved.
//

import UIKit

//Error is for this line

class TransitionAnimator: NSObject, UIViewControllerAnimatedTransitioning{

    weak var transitionContext: UIViewControllerContextTransitioning?


    func animateTransition(transitionContext: UIViewControllerContextTransitioning) {

        //1
        self.transitionContext = transitionContext

        //2
        var containerView = transitionContext.containerView()
        var fromViewController = transitionContext.viewControllerForKey(UITransitionContextFromViewControllerKey) as! ViewController
        var toViewController = transitionContext.viewControllerForKey(UITransitionContextToViewControllerKey) as! ViewController
        var button = fromViewController.btn2

        //3
        containerView.addSubview(toViewController.view)

        //4
        var circleMaskPathInitial = UIBezierPath(ovalInRect: button.frame)
        var extremePoint = CGPoint(x: button.center.x - 0, y: button.center.y - CGRectGetHeight(toViewController.view.bounds))
        var radius = sqrt((extremePoint.x*extremePoint.x) + (extremePoint.y*extremePoint.y))
        var circleMaskPathFinal = UIBezierPath(ovalInRect: CGRectInset(button.frame, -radius, -radius))

        //5
        var maskLayer = CAShapeLayer()
        maskLayer.path = circleMaskPathFinal.CGPath
        toViewController.view.layer.mask = maskLayer

        //6
        var maskLayerAnimation = CABasicAnimation(keyPath: "path")
        maskLayerAnimation.fromValue = circleMaskPathInitial.CGPath
        maskLayerAnimation.toValue = circleMaskPathFinal.CGPath

/*also get an error here "TransitionAnimator does not have a member named 'transitionDuration' " */

maskLayerAnimation.duration = self.transitionDuration(transitionContext)
        maskLayerAnimation.delegate = self
        maskLayer.addAnimation(maskLayerAnimation, forKey: "path")

    }

    override func animationDidStop(anim: CAAnimation!, finished flag: Bool) {
        self.transitionContext?.completeTransition(!self.transitionContext!.transitionWasCancelled())
        self.transitionContext?.viewControllerForKey(UITransitionContextFromViewControllerKey)?.view.layer.mask = nil
    }

}